1. Field of the Invention
This invention relates to a catheter assembly, and more particularly to a catheter assembly through which an optical fiber passes.
2. Description of Related Art
Fiberoptic catheter assemblies have been increasingly used in clearing obstructions from the pathways of various vessels, such as arteries. The size of the vessels from which the obstruction must be removed determines the size of the catheter which can be placed inside the vessel. Therefore, in certain applications, a catheter with a very small diameter is necessary. However, because of the winding path of various vessels, the catheter must be steerable so that the obstruction can be reached. Once reached, a laser may then provide energy which is transmitted by the optical fiber to ablate the obstruction.
For smaller vessels, a catheter which houses both a guide wire and an optical fiber can be used to advance the catheter assembly to the obstruction in the vessel without causing a perforation of the vessel wall. This has been shown in Anderson, et al.: Steerable Fiberoptic Catheter Delivery of Laser Energy in Atherosclerotic Rabbits, Am. Heart J., 111:1065, 1986. The assembly disclosed in the Anderson article shows a catheter with a single lumen which houses both the guide wire and the optical fiber. The hole of the lumen in the Anderson article is also of a large enough diameter to allow for contrast and saline solutions to be injected through the lumen while the optical fiber and guide wire are also running through the lumen. Because of this configuration, the Anderson assembly can only be assured of removing obstructive material from an area directly in front of the tip of the optical fiber. Rotation of the catheter assembly will not necessarily cause the optical fiber to rotate, because the optical fiber and guide wire may simply become twisted within the lumen as the catheter rotates. In fact, the Anderson reference does not even suggest that the catheter assembly be rotated. Even if the fiber rotates, rotation of the catheter assembly will not necessarily result in a maximized ablated area, without leaving a central core of material, since the fiber is not carefully located eccentrically, covering the center of the catheter.
It is also known that fibers with polished, flat-tipped distal ends can easily perforate vessel walls. Sapphire contact probes and quartz shield-tipped catheters have been developed which utilize round, smooth-tipped configurations. This configuration reduces the risk of perforations to the vessel wall by the optical fiber. However, the sapphire contact probes and the quartz shield-tipped catheters currently available have the drawback of having a diameter which is too large to be used in smaller vessels, such as coronary arteries. These devices also require the coupling of a separate tip to the fiber. This coupling causes a greater loss in energy which can be delivered to the obstruction.
A catheter which uses emitted laser energy and is capable of being rotated is also disclosed in U.S. Pat. No. 4,627,436 by Leckrone. For operation, the device must pass the obstruction so that laser energy can emerge from a fiber in the periphery of the cylinder of the catheter to the obstruction. By using laser energy in this way, the periphery of the catheter must be fitted with abutments on the exterior of the catheter periphery, which prevent laser energy from being transmitted outside the abutments. The abutments also encompass the obstruction so that once the obstruction is ablated, it can be suctioned back to the proximal end of the catheter. Since the device must first pass the obstruction, the device is limited to subtotal obstructions which cover a small enough area of the vessel to allow passage of the device. Proper positioning of this device also requires expansion of a balloon to make sure that the abutments are properly placed.
This known art does not disclose how to deliver a beam of energy which is large enough to ablate a large percentage of an obstruction which is in a narrow vessel. An optical fiber with a larger diameter does not have the flexibility required to pass through turns of the vessels. Optical fibers with a small diameter that can be used with a guide wire have only been able to clear obstructions directly in front of the tip of the optical fiber. The present invention overcomes these difficulties to provide for clearing a much greater percentage of the obstruction that is in the vessel.